All we need to do is to divide the number of eligible voters by 62% to find out how many people have been registered:
55200 ÷ 62% =
= 55200 ÷ 62/100 =
= 55200 * 100/62 =
= 5520000 / 62 =
= 89032,25806451613 ≈ (note the rounding to the nearest whole number)
≈ 89032
Doublecheck:
89032 * 62% =
= 89032 * 62/100 =
= 5519984 / 100 =
= 55199,84 ≈ (the difference is because of the rounding before)
≈ 55200
Answer: There were 89,032 people registered.